As illustrated in FIG. 1 which is a schematic diagram of a network architecture of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), the E-UTRAN is composed of evolved Node Bs (eNBs).
A Mobility Management Entity (MME) and an eNB are connected via an S1-MME interface; and the eNB achieves the network access function and communicates with a User Equipment (UE) via an air interface. For each UE attached to the network, there is an MME serving the UE, and the MME is referred to as a serving MME of the UE. The S1-MME interface provides the UE with a control plane service, including mobility management and bearer management functions.
A Serving Gateway (S-GW) and the eNB is connected via an S1-U interface, and for each UE attached to the network, there is an S-GW serving the UE, where the S-GW is referred to as a serving S-GW of the UE. The S1-U interface provides the UE with a user plane service, and user plane data of the UE is transmitted between the S-GW and the eNB over a S1-U General Packet Radio Service (GPRS) Tunneling Protocol (GTP) bearer.
FIG. 2 illustrates a user plane protocol stack between the UE and the network, and FIG. 3 illustrates a control plane protocol stack, where user plane protocols include Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC) and physical layer (PHY); and control plane protocols include Radio Resource Control (RRC) and Non-Access Stratum (NAS) layer, where an RRC layer message needs to be processed at the user plane protocol layer and then transmitted on an air interface; an NAS layer message is transmitted on an air interface by being encapsulated in an RRC message; and on an S1-MME interface transmission is performed over an S1 connection.
In an existing LTE/LTE-A network, all of RRC/RDCP/RLC/MAC/PHY peer layers of the UE are located in the same eNB, and an NAS peer layer of the UE is located in an MME established with the eNB an S1 connection for the UE.
In the existing protocol, PDCP and RLC entities correspond to a Data Radio Bearer (DRB)/Signaling Radio Bearer (SRB) 1/SRB2, and each DRB/SRB1/SRB2 corresponds to a set of PDCP and RLC entities; and the DRB/SRB1/SRB2 are converged at the MAC layer. Thus there may be multiple sets of PDCP and RLC entities but only one MAC layer and physical layer entities for the UE. The SRB is a control plane bearer, and the DRB is a user plane bearer.
In an existing layered network as illustrated in FIG. 4, a macro cell provides underlying coverage, a Local Cell provides hotspot coverage, there is a data/signaling interface (wired/wireless interface) between the Local Cell and the Macro Cell, and the UE may operate in a macro eNB or a local eNB.
Due to a small coverage of, and a small number of UEs, served by the cell controlled by the local eNB, the UEs connected with the local eNB tend to be provided with a better quality of service, e.g., a higher rate for service, a link with a higher quality, etc. Thus when the UE connected with the macro eNB is close to the cell controlled by the local eNB, the UE can be switched to the local eNB to be served by the local eNB; and when the UE is far away from the cell controlled by the local eNB, the UE needs to be switched to the cell controlled by the macro eNB to keep wireless connection. As the number of local eNBs with small coverage is large, the UE has to be switched frequently between the macro eNB cell and the local eNB cell. For a UE, both the switch frequency and the number of times of the switch are greatly increased so that a risk of interruption of communications of the UE being switched is increased.
In summary, currently in the network architecture of the E-UTRAN, both the switch frequency and the number of times of the switch for a UE are greatly increased so that a risk of interruption of communications of the UE being switched is increased.